1. Field of the Invention
The present invention relates to a high-frequency module that transmits and receives high-frequency signals with a plurality of frequencies including a single antenna.
2. Description of the Related Art
With increasing performance and decreasing sizes of radio frequency communication apparatuses, such as mobile phones, a circuit for transmitting and receiving communication signals having high frequencies in different frequency bands by sharing a single antenna is required. Various types of triplexers for transmitting and receiving three different types of communication signal have been proposed as such a circuit.
For example, in the triplexer described in Japanese Unexamined Patent Application Publication No. 2006-332980, a low pass filter, a band pass filter, and a high pass filter are connected in parallel to common terminals, where the passbands of the respective filters are different from one another. Among three types of communication signals, the low pass filter allows communication signals in the lowest frequency band to pass therethrough, the high pass filter allows communication signals in the highest frequency band to pass therethrough, and the band pass filter allows communication signals in an intermediate frequency band to pass therethrough. Each filter attenuates communication signals in frequency bands other than its own frequency band.
When communication signals in a plurality of frequency bands are transmitted and received, particularly when the frequency bands of the communication signals are close to one another, not only transmission characteristics of a passband, but also attenuation characteristics in bands other than the passband need to be improved in each filter in order to allow only desired communication signals to pass. One of the methods of improving the attenuation characteristics is to set an attenuation pole using a resonance of an inductor and a capacitor near a passband. The use of this method allows attenuation characteristics near the passband to be improved as illustrated in FIG. 3 of Japanese Unexamined Patent Application Publication No. 2006-332980.
However, as shown in FIG. 3 of Japanese Unexamined Patent Application Publication No. 2006-332980, in the method of providing an attenuation pole, a low attenuation frequency band, i.e., a rebound band due to an attenuation pole, is generated in a frequency range which is farther from the passband than the attenuation pole. When such a frequency band with low attenuation outside of the passband overlaps the frequency band of another communication signal, this communication signal, which is supposed to be attenuated, is allowed to pass.